The presently disclosed embodiments relate generally to a process for producing emulsion aggregation (EA) toners suitable for electrostatographic apparatuses.
Numerous processes are within the purview of those skilled in the art for the preparation of EA toners. These toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
EA toner processes include coagulating a combination of emulsions, i.e., emulsions each including, independent of one another or meaning that they can be the same or different, a latex, wax, pigment, and the like, with a flocculent such as polyaluminum chloride and/or aluminum sulfate, to generate a slurry of primary aggregates which then undergoes a controlled aggregation process. The solid content of this primary slurry dictates the overall throughput of the EA toner process. While an even higher solids content may be desirable, it may be difficult to achieve due to high viscosity of the emulsions and poor mixing, which may lead to the formation of unacceptable primary aggregates (high coarse particle content).
Current EA toner processes require the addition of flocculent while homogenizing with an IKA homogenizer for small scale production or through an in-line cavitron homogenizer for large scale production. Regardless of scale, homogenization is necessary to ensure a well-distributed flocculent addition resulting in small particle sizes, narrow distributions, and <1% coarse (>16 micron). This then translates to a final toner product complying with <1% coarse (>16 micron) specification. Typically, at the manufacturing scale, the homogenization step requires a minimum of 60 to 90 minutes which results in an overall 8 hours to produce EA toner. Other drawbacks with the current process include flocculent addition errors when dealing with pumping in the flocculent via a homogenizer. Often, the rate of pumping in flocculent is too rapid, or there are leakages. Also the current rotor-stator homogenizer generates about 10-15° C. heat. Thus, it is desirable to reduce the homogenization time (either by not producing the large agglomerates or finding a more effective flocculent distribution method) in order to reduce the overall toner cycle time and the amount of energy used. It is also desirable to reduce production costs for such toners and seek more environmentally friendly processes by reducing leakage of flocculent.
Improved methods for producing toners, which reduce the number of stages and materials, remain desirable. Acoustic mixing is a new approach to mixing and dispersion of materials ranging from nanoparticle suspensions to viscous gels. It is distinct from conventional impeller agitation found in a planetary mixer or speed mixer as well as ultrasonic mixing. Low frequency, high-intensity acoustic energy is used to create a uniform shear field throughout the entire mixing vessel. The result is rapid fluidization (like a fluidized bed) and dispersion of material. This invention proposes a new and effective flocculent distribution method and process for breaking toner particles with acoustic mixer using low-frequency, high intensity acoustic energy. By using an acoustic mixer, the toner slurry and flocculent can be mixed together and a good distribution of flocculent can be achieved in five (5) minutes, drastically reducing toner cycle time by about 17.8%. In addition, acoustic mixers come in a variety of sizes from a bench top model (roughly 500 milliliters) to manufacturing scale (30 gallons), which enables implantation of this process for both small and large scale purposes.
Another advantage of such process is that flocculent is now added directly to the slurry before acoustic mixing which reduces the need to pump in flocculent via a homogenizer. As such, there are no leaks as there is no need for material to flow through equipment. Further, the acoustic mixer does not generate any heat and thus, this process can be utilized for heat-sensitive materials.